Bombers killed at least 137 worshipers and wounded hundreds more during Friday prayers at two mosques in the Yemeni capital Sanaa, in coordinated attacks claimed by Islamic State.

The attacks on mosques used by supporters of the Shi’ite Muslim Houthi fighters who control the city were the deadliest in a years-long campaign of violence in the country, where Washington has been waging a drone air war against a local branch of the Sunni Muslim militant group al-Qaida.

Amid the CNN report, Yemen’s President Abd-Rabbu Mansour Hadi on Saturday called on the Houthi militia to leave the capital Sanaa and for its allied militias to quit government ministries in his first televised speech since escaping house arrest last month.

Hadi urged all parties in Yemen to attend peace talks in the Saudi Arabian capital Riyadh, but also vowed to plant the national flag in the Houthi stronghold of Saadeh, in a comment the group is likely to interpret as a call to arms.

The Shi’ite Muslim Houthis, who are allied to Iran, seized Sanaa in September and then besieged Hadi’s residence in January, leading him to offer his resignation and resulting in his house arrest by the group before he escaped to Aden last month.

Hadi and the Houthis have since then commanded rival power centers in north and south Yemen, leading to fears of a full-scale civil war, and giving Sunni Muslim jihadist groups such as al-Qaida more space to operate.

Hadi said Yemen must return to the political situation in place before the Houthis took control of Sanaa, re-instituting its constitution and implementing the results of a national dialogue process and Gulf-sponsored political transition.

In his speech, he denounced the Houthis as “coup plotters” and said he wanted to confront sectarianism. Addressing Houthi accusations that he planned to back a southern secessionist movement, he said his flight to Aden had been intended to preserve Yemeni unity.